Southern California is notorious for its smog, but just a few hundred miles away in the High Sierras, the air is much cleaner. To demonstrate the difference, researchers Aaron Reuben and Gabriel Isaacman of Yale Center for Environmental Policy and University of California Berkeley took pollutant compounds from air samples to create a sound spectrum of California’s ‘cleaner’ and ‘dirtier’ locations to help understand the way we breathe. You can actually hear the difference between clean air and smog!

The soundscape was created by taking air samples and using gas chromotograpy to separate out the thousands of compounds in the air. Reuben and Isaacman then used mass spectometry to plot the chemicals based on structure, before categorizing the compounds and mapping them on a spectrum based on a ratio of mass-to-charge. They then assigned tones to each of the compounds allowing them to, in essence, ‘hear the pollution.’

In order to see how smog sounded in different areas, the two researchers took air samples from assorted sites around California that are renowned for either their high or low pollution. They discovered that in areas of high pollution, the soundscape emitted a low droning sound, which was due to the large amount of ‘heavy’ hydrocarbons. In less polluted areas, they heard sounds that were higher in pitch and with more frequent chirps.

“Some compounds end up sounding clear and distinct, while others blur together into unresolvable chords,” explains Aaron Rueben in The Atlantic. “The result is a qualitative, sensory experience of hard, digital data. You can actually hear the difference between the toxic air of a truck tunnel (clogged with diesel hydrocarbons and carcinogenic particulate matter) and the fragrant air of the High Sierras.”

In fact, click below to hear the difference between the Caldecott Tunnel in Oakland and the High Sierras. You can hear the air pollution of other areas in California here.